Insecticidal metabolites from Serratia marcescens associated with the fall armyworm (Spodoptera frugiperda): molecular identification, metabolomic profiling and molecular docking insights.

The fall armyworm (S. frugiperda) has developed resistance to numerous insecticides and is currently considered one of the most destructive pests threatening global crop production. Consequently, the development of environmentally sustainable pest management strategies has become increasingly important. Insect-associated pathogenic bacteria represent a promising source of bioactive metabolites with potential insecticidal properties. In the present study, pathogenic bacteria associated with S. frugiperda were isolated and molecularly identified as Serratia marcescens strain INS420 based on 16 S rRNA gene sequencing. The secondary metabolites produced by this bacterium demonstrated significant insecticidal activity under both laboratory and field conditions. Metabolic profiling of the extracted compounds was performed using liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS), revealing the presence of several bioactive compounds, including diketopiperazines, fatty acids and their esters, squalene, phthalate derivatives, and a cardenolide. To gain insights into the potential mechanism of action, molecular docking simulations were conducted to evaluate the binding affinity of the identified metabolites with S. frugiperda acetylcholinesterase (AChE). Among the detected compounds, squalene and several fatty acid derivatives exhibited stable interactions within the active site of the enzyme, suggesting a possible inhibitory effect on AChE activity. Collectively, these findings demonstrate that S. marcescens associated with S. frugiperda produces metabolites with notable insecticidal potential and highlight insect-associated pathogenic bacteria as a valuable source of bioactive compounds for the sustainable management of fall armyworm.